Among various conventional refrigeration systems including a refrigerant circuit operable in a vapor compression refrigeration cycle, there are known refrigeration systems having the function of analyzing their own condition. Refrigeration systems of such kind are configured to analyze their own condition by comparing an operating condition determined from detected values such as of temperature sensors and pressure sensors with a normal operating condition.
Specifically, Patent Document 1 discloses an air conditioner using Mollier diagrams showing the relation between pressure and enthalpy to analyze the condition of the refrigeration system and thereby diagnose whether its component devices are normal or defective. The air conditioner includes as component devices of its outdoor unit a compressor, a four-way selector valve and an outdoor heat exchanger and includes as a component device of its indoor unit an indoor heat exchanger. Furthermore, a diagnoser (controller) for the air conditioner includes a numerical value conversion means, a first input means, a first characteristic calculation means, a second characteristic calculation means, a characteristic diagnosis means and a result display means.
When in the above air conditioner the diagnoser outputs a diagnosis start instruction, the numerical value conversion means first converts the voltage values of temperatures and pressures detected by temperature sensors and pressure sensors to numerical values. Furthermore, by means of the first input means, the respective amounts of refrigerant in the outdoor and indoor units, the length of the connecting pipe and other data are input. Next, the first characteristic calculation means makes a Mollier diagram of the air conditioner in a normal condition based on data obtained from the first input means and the numerical value conversion means. Next, the second characteristic calculation means makes a Mollier diagram of the air conditioner in operation. Then, the characteristic diagnosis means compares the Mollier diagram in the normal condition from the first characteristic calculation means with the Mollier diagram in operation from the second characteristic calculation means to identify a place of failure or a reason for failure. Then, the result display means displays details of the diagnosis of the characteristic diagnosis means.    Patent Document 1: Published Japanese Patent Application No. 2001-133011